/*
 * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 *
 *
 *
 *
 */

package java.lang;

import java.util.Arrays;

/**
 * A thread-safe, mutable sequence of characters.
 * A string buffer is like a {@link String}, but can be modified. At any
 * point in time it contains some particular sequence of characters, but
 * the length and content of the sequence can be changed through certain
 * method calls.
 * <p>
 * String buffers are safe for use by multiple threads. The methods
 * are synchronized where necessary so that all the operations on any
 * particular instance behave as if they occur in some serial order
 * that is consistent with the order of the method calls made by each of
 * the individual threads involved.
 * <p>
 * The principal operations on a {@code StringBuffer} are the
 * {@code append} and {@code insert} methods, which are
 * overloaded so as to accept data of any type. Each effectively
 * converts a given datum to a string and then appends or inserts the
 * characters of that string to the string buffer. The
 * {@code append} method always adds these characters at the end
 * of the buffer; the {@code insert} method adds the characters at
 * a specified point.
 * <p>
 * For example, if {@code z} refers to a string buffer object
 * whose current contents are {@code "start"}, then
 * the method call {@code z.append("le")} would cause the string
 * buffer to contain {@code "startle"}, whereas
 * {@code z.insert(4, "le")} would alter the string buffer to
 * contain {@code "starlet"}.
 * <p>
 * In general, if sb refers to an instance of a {@code StringBuffer},
 * then {@code sb.append(x)} has the same effect as
 * {@code sb.insert(sb.length(), x)}.
 * <p>
 * Whenever an operation occurs involving a source sequence (such as
 * appending or inserting from a source sequence), this class synchronizes
 * only on the string buffer performing the operation, not on the source.
 * Note that while {@code StringBuffer} is designed to be safe to use
 * concurrently from multiple threads, if the constructor or the
 * {@code append} or {@code insert} operation is passed a source sequence
 * that is shared across threads, the calling code must ensure
 * that the operation has a consistent and unchanging view of the source
 * sequence for the duration of the operation.
 * This could be satisfied by the caller holding a lock during the
 * operation's call, by using an immutable source sequence, or by not
 * sharing the source sequence across threads.
 * <p>
 * Every string buffer has a capacity. As long as the length of the
 * character sequence contained in the string buffer does not exceed
 * the capacity, it is not necessary to allocate a new internal
 * buffer array. If the internal buffer overflows, it is
 * automatically made larger.
 * <p>
 * Unless otherwise noted, passing a {@code null} argument to a constructor
 * or method in this class will cause a {@link NullPointerException} to be
 * thrown.
 * <p>
 * As of  release JDK 5, this class has been supplemented with an equivalent
 * class designed for use by a single thread, {@link StringBuilder}.  The
 * {@code StringBuilder} class should generally be used in preference to
 * this one, as it supports all of the same operations but it is faster, as
 * it performs no synchronization.
 *
 * @author Arthur van Hoff
 * @see java.lang.StringBuilder
 * @see java.lang.String
 * @since JDK1.0
 */
public final class StringBuffer
    extends AbstractStringBuilder
    implements java.io.Serializable, CharSequence {

  /**
   * A cache of the last value returned by toString. Cleared
   * whenever the StringBuffer is modified.
   */
  private transient char[] toStringCache;

  /**
   * use serialVersionUID from JDK 1.0.2 for interoperability
   */
  static final long serialVersionUID = 3388685877147921107L;

  /**
   * Constructs a string buffer with no characters in it and an
   * initial capacity of 16 characters.
   */
  public StringBuffer() {
    super(16);
  }

  /**
   * Constructs a string buffer with no characters in it and
   * the specified initial capacity.
   *
   * @param capacity the initial capacity.
   * @throws NegativeArraySizeException if the {@code capacity} argument is less than {@code 0}.
   */
  public StringBuffer(int capacity) {
    super(capacity);
  }

  /**
   * Constructs a string buffer initialized to the contents of the
   * specified string. The initial capacity of the string buffer is
   * {@code 16} plus the length of the string argument.
   *
   * @param str the initial contents of the buffer.
   */
  public StringBuffer(String str) {
    super(str.length() + 16);
    append(str);
  }

  /**
   * Constructs a string buffer that contains the same characters
   * as the specified {@code CharSequence}. The initial capacity of
   * the string buffer is {@code 16} plus the length of the
   * {@code CharSequence} argument.
   * <p>
   * If the length of the specified {@code CharSequence} is
   * less than or equal to zero, then an empty buffer of capacity
   * {@code 16} is returned.
   *
   * @param seq the sequence to copy.
   * @since 1.5
   */
  public StringBuffer(CharSequence seq) {
    this(seq.length() + 16);
    append(seq);
  }

  @Override
  public synchronized int length() {
    return count;
  }

  @Override
  public synchronized int capacity() {
    return value.length;
  }


  @Override
  public synchronized void ensureCapacity(int minimumCapacity) {
    if (minimumCapacity > value.length) {
      expandCapacity(minimumCapacity);
    }
  }

  /**
   * @since 1.5
   */
  @Override
  public synchronized void trimToSize() {
    super.trimToSize();
  }

  /**
   * @throws IndexOutOfBoundsException {@inheritDoc}
   * @see #length()
   */
  @Override
  public synchronized void setLength(int newLength) {
    toStringCache = null;
    super.setLength(newLength);
  }

  /**
   * @throws IndexOutOfBoundsException {@inheritDoc}
   * @see #length()
   */
  @Override
  public synchronized char charAt(int index) {
    if ((index < 0) || (index >= count)) {
      throw new StringIndexOutOfBoundsException(index);
    }
    return value[index];
  }

  /**
   * @since 1.5
   */
  @Override
  public synchronized int codePointAt(int index) {
    return super.codePointAt(index);
  }

  /**
   * @since 1.5
   */
  @Override
  public synchronized int codePointBefore(int index) {
    return super.codePointBefore(index);
  }

  /**
   * @since 1.5
   */
  @Override
  public synchronized int codePointCount(int beginIndex, int endIndex) {
    return super.codePointCount(beginIndex, endIndex);
  }

  /**
   * @since 1.5
   */
  @Override
  public synchronized int offsetByCodePoints(int index, int codePointOffset) {
    return super.offsetByCodePoints(index, codePointOffset);
  }

  /**
   * @throws IndexOutOfBoundsException {@inheritDoc}
   */
  @Override
  public synchronized void getChars(int srcBegin, int srcEnd, char[] dst,
      int dstBegin) {
    super.getChars(srcBegin, srcEnd, dst, dstBegin);
  }

  /**
   * @throws IndexOutOfBoundsException {@inheritDoc}
   * @see #length()
   */
  @Override
  public synchronized void setCharAt(int index, char ch) {
    if ((index < 0) || (index >= count)) {
      throw new StringIndexOutOfBoundsException(index);
    }
    toStringCache = null;
    value[index] = ch;
  }

  @Override
  public synchronized StringBuffer append(Object obj) {
    toStringCache = null;
    super.append(String.valueOf(obj));
    return this;
  }

  @Override
  public synchronized StringBuffer append(String str) {
    toStringCache = null;
    super.append(str);
    return this;
  }

  /**
   * Appends the specified {@code StringBuffer} to this sequence.
   * <p>
   * The characters of the {@code StringBuffer} argument are appended,
   * in order, to the contents of this {@code StringBuffer}, increasing the
   * length of this {@code StringBuffer} by the length of the argument.
   * If {@code sb} is {@code null}, then the four characters
   * {@code "null"} are appended to this {@code StringBuffer}.
   * <p>
   * Let <i>n</i> be the length of the old character sequence, the one
   * contained in the {@code StringBuffer} just prior to execution of the
   * {@code append} method. Then the character at index <i>k</i> in
   * the new character sequence is equal to the character at index <i>k</i>
   * in the old character sequence, if <i>k</i> is less than <i>n</i>;
   * otherwise, it is equal to the character at index <i>k-n</i> in the
   * argument {@code sb}.
   * <p>
   * This method synchronizes on {@code this}, the destination
   * object, but does not synchronize on the source ({@code sb}).
   *
   * @param sb the {@code StringBuffer} to append.
   * @return a reference to this object.
   * @since 1.4
   */
  public synchronized StringBuffer append(StringBuffer sb) {
    toStringCache = null;
    super.append(sb);
    return this;
  }

  /**
   * @since 1.8
   */
  @Override
  synchronized StringBuffer append(AbstractStringBuilder asb) {
    toStringCache = null;
    super.append(asb);
    return this;
  }

  /**
   * Appends the specified {@code CharSequence} to this
   * sequence.
   * <p>
   * The characters of the {@code CharSequence} argument are appended,
   * in order, increasing the length of this sequence by the length of the
   * argument.
   *
   * <p>The result of this method is exactly the same as if it were an
   * invocation of this.append(s, 0, s.length());
   *
   * <p>This method synchronizes on {@code this}, the destination
   * object, but does not synchronize on the source ({@code s}).
   *
   * <p>If {@code s} is {@code null}, then the four characters
   * {@code "null"} are appended.
   *
   * @param s the {@code CharSequence} to append.
   * @return a reference to this object.
   * @since 1.5
   */
  @Override
  public synchronized StringBuffer append(CharSequence s) {
    toStringCache = null;
    super.append(s);
    return this;
  }

  /**
   * @throws IndexOutOfBoundsException {@inheritDoc}
   * @since 1.5
   */
  @Override
  public synchronized StringBuffer append(CharSequence s, int start, int end) {
    toStringCache = null;
    super.append(s, start, end);
    return this;
  }

  @Override
  public synchronized StringBuffer append(char[] str) {
    toStringCache = null;
    super.append(str);
    return this;
  }

  /**
   * @throws IndexOutOfBoundsException {@inheritDoc}
   */
  @Override
  public synchronized StringBuffer append(char[] str, int offset, int len) {
    toStringCache = null;
    super.append(str, offset, len);
    return this;
  }

  @Override
  public synchronized StringBuffer append(boolean b) {
    toStringCache = null;
    super.append(b);
    return this;
  }

  @Override
  public synchronized StringBuffer append(char c) {
    toStringCache = null;
    super.append(c);
    return this;
  }

  @Override
  public synchronized StringBuffer append(int i) {
    toStringCache = null;
    super.append(i);
    return this;
  }

  /**
   * @since 1.5
   */
  @Override
  public synchronized StringBuffer appendCodePoint(int codePoint) {
    toStringCache = null;
    super.appendCodePoint(codePoint);
    return this;
  }

  @Override
  public synchronized StringBuffer append(long lng) {
    toStringCache = null;
    super.append(lng);
    return this;
  }

  @Override
  public synchronized StringBuffer append(float f) {
    toStringCache = null;
    super.append(f);
    return this;
  }

  @Override
  public synchronized StringBuffer append(double d) {
    toStringCache = null;
    super.append(d);
    return this;
  }

  /**
   * @throws StringIndexOutOfBoundsException {@inheritDoc}
   * @since 1.2
   */
  @Override
  public synchronized StringBuffer delete(int start, int end) {
    toStringCache = null;
    super.delete(start, end);
    return this;
  }

  /**
   * @throws StringIndexOutOfBoundsException {@inheritDoc}
   * @since 1.2
   */
  @Override
  public synchronized StringBuffer deleteCharAt(int index) {
    toStringCache = null;
    super.deleteCharAt(index);
    return this;
  }

  /**
   * @throws StringIndexOutOfBoundsException {@inheritDoc}
   * @since 1.2
   */
  @Override
  public synchronized StringBuffer replace(int start, int end, String str) {
    toStringCache = null;
    super.replace(start, end, str);
    return this;
  }

  /**
   * @throws StringIndexOutOfBoundsException {@inheritDoc}
   * @since 1.2
   */
  @Override
  public synchronized String substring(int start) {
    return substring(start, count);
  }

  /**
   * @throws IndexOutOfBoundsException {@inheritDoc}
   * @since 1.4
   */
  @Override
  public synchronized CharSequence subSequence(int start, int end) {
    return super.substring(start, end);
  }

  /**
   * @throws StringIndexOutOfBoundsException {@inheritDoc}
   * @since 1.2
   */
  @Override
  public synchronized String substring(int start, int end) {
    return super.substring(start, end);
  }

  /**
   * @throws StringIndexOutOfBoundsException {@inheritDoc}
   * @since 1.2
   */
  @Override
  public synchronized StringBuffer insert(int index, char[] str, int offset,
      int len) {
    toStringCache = null;
    super.insert(index, str, offset, len);
    return this;
  }

  /**
   * @throws StringIndexOutOfBoundsException {@inheritDoc}
   */
  @Override
  public synchronized StringBuffer insert(int offset, Object obj) {
    toStringCache = null;
    super.insert(offset, String.valueOf(obj));
    return this;
  }

  /**
   * @throws StringIndexOutOfBoundsException {@inheritDoc}
   */
  @Override
  public synchronized StringBuffer insert(int offset, String str) {
    toStringCache = null;
    super.insert(offset, str);
    return this;
  }

  /**
   * @throws StringIndexOutOfBoundsException {@inheritDoc}
   */
  @Override
  public synchronized StringBuffer insert(int offset, char[] str) {
    toStringCache = null;
    super.insert(offset, str);
    return this;
  }

  /**
   * @throws IndexOutOfBoundsException {@inheritDoc}
   * @since 1.5
   */
  @Override
  public StringBuffer insert(int dstOffset, CharSequence s) {
    // Note, synchronization achieved via invocations of other StringBuffer methods
    // after narrowing of s to specific type
    // Ditto for toStringCache clearing
    super.insert(dstOffset, s);
    return this;
  }

  /**
   * @throws IndexOutOfBoundsException {@inheritDoc}
   * @since 1.5
   */
  @Override
  public synchronized StringBuffer insert(int dstOffset, CharSequence s,
      int start, int end) {
    toStringCache = null;
    super.insert(dstOffset, s, start, end);
    return this;
  }

  /**
   * @throws StringIndexOutOfBoundsException {@inheritDoc}
   */
  @Override
  public StringBuffer insert(int offset, boolean b) {
    // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
    // after conversion of b to String by super class method
    // Ditto for toStringCache clearing
    super.insert(offset, b);
    return this;
  }

  /**
   * @throws IndexOutOfBoundsException {@inheritDoc}
   */
  @Override
  public synchronized StringBuffer insert(int offset, char c) {
    toStringCache = null;
    super.insert(offset, c);
    return this;
  }

  /**
   * @throws StringIndexOutOfBoundsException {@inheritDoc}
   */
  @Override
  public StringBuffer insert(int offset, int i) {
    // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
    // after conversion of i to String by super class method
    // Ditto for toStringCache clearing
    super.insert(offset, i);
    return this;
  }

  /**
   * @throws StringIndexOutOfBoundsException {@inheritDoc}
   */
  @Override
  public StringBuffer insert(int offset, long l) {
    // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
    // after conversion of l to String by super class method
    // Ditto for toStringCache clearing
    super.insert(offset, l);
    return this;
  }

  /**
   * @throws StringIndexOutOfBoundsException {@inheritDoc}
   */
  @Override
  public StringBuffer insert(int offset, float f) {
    // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
    // after conversion of f to String by super class method
    // Ditto for toStringCache clearing
    super.insert(offset, f);
    return this;
  }

  /**
   * @throws StringIndexOutOfBoundsException {@inheritDoc}
   */
  @Override
  public StringBuffer insert(int offset, double d) {
    // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
    // after conversion of d to String by super class method
    // Ditto for toStringCache clearing
    super.insert(offset, d);
    return this;
  }

  /**
   * @since 1.4
   */
  @Override
  public int indexOf(String str) {
    // Note, synchronization achieved via invocations of other StringBuffer methods
    return super.indexOf(str);
  }

  /**
   * @since 1.4
   */
  @Override
  public synchronized int indexOf(String str, int fromIndex) {
    return super.indexOf(str, fromIndex);
  }

  /**
   * @since 1.4
   */
  @Override
  public int lastIndexOf(String str) {
    // Note, synchronization achieved via invocations of other StringBuffer methods
    return lastIndexOf(str, count);
  }

  /**
   * @since 1.4
   */
  @Override
  public synchronized int lastIndexOf(String str, int fromIndex) {
    return super.lastIndexOf(str, fromIndex);
  }

  /**
   * @since JDK1.0.2
   */
  @Override
  public synchronized StringBuffer reverse() {
    toStringCache = null;
    super.reverse();
    return this;
  }

  @Override
  public synchronized String toString() {
    if (toStringCache == null) {
      toStringCache = Arrays.copyOfRange(value, 0, count);
    }
    return new String(toStringCache, true);
  }

  /**
   * Serializable fields for StringBuffer.
   *
   * @serialField value  char[] The backing character array of this StringBuffer.
   * @serialField count int The number of characters in this StringBuffer.
   * @serialField shared  boolean A flag indicating whether the backing array is shared. The value
   * is ignored upon deserialization.
   */
  private static final java.io.ObjectStreamField[] serialPersistentFields =
      {
          new java.io.ObjectStreamField("value", char[].class),
          new java.io.ObjectStreamField("count", Integer.TYPE),
          new java.io.ObjectStreamField("shared", Boolean.TYPE),
      };

  /**
   * readObject is called to restore the state of the StringBuffer from
   * a stream.
   */
  private synchronized void writeObject(java.io.ObjectOutputStream s)
      throws java.io.IOException {
    java.io.ObjectOutputStream.PutField fields = s.putFields();
    fields.put("value", value);
    fields.put("count", count);
    fields.put("shared", false);
    s.writeFields();
  }

  /**
   * readObject is called to restore the state of the StringBuffer from
   * a stream.
   */
  private void readObject(java.io.ObjectInputStream s)
      throws java.io.IOException, ClassNotFoundException {
    java.io.ObjectInputStream.GetField fields = s.readFields();
    value = (char[]) fields.get("value", null);
    count = fields.get("count", 0);
  }
}
